.TH std::vprintf,std::vfprintf,std::vsprintf,std::vsnprintf 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::vprintf,std::vfprintf,std::vsprintf,std::vsnprintf \- std::vprintf,std::vfprintf,std::vsprintf,std::vsnprintf

.SH Synopsis
   Defined in header <cstdio>
   int vprintf( const char* format, std::va_list vlist );             \fB(1)\fP
   int vfprintf( std::FILE* stream, const char* format, std::va_list  \fB(2)\fP
   vlist );
   int vsprintf( char* buffer, const char* format, std::va_list vlist \fB(3)\fP
   );
   int vsnprintf( char* buffer, std::size_t buf_size, const char*     \fB(4)\fP \fI(since C++11)\fP
   format, std::va_list vlist );

   Loads the data from the locations, defined by vlist, converts them to character
   string equivalents and writes the results to a variety of sinks.

   1) Writes the results to stdout.
   2) Writes the results to a file stream stream.
   3) Writes the results to a character string buffer.
   4) Writes the results to a character string buffer. At most buf_size - 1 characters
   are written. The resulting character string will be terminated with a null
   character, unless buf_size is zero. If buf_size is zero, nothing is written and
   buffer may be a null pointer, however the return value (number of bytes that would
   be written not including the null terminator) is still calculated and returned.

.SH Parameters

   stream   - output file stream to write to
   buffer   - pointer to a character string to write to
   buf_size - maximum number of characters to write
   format   - pointer to a null-terminated character string specifying how to interpret
              the data
   vlist    - variable argument list containing the data to print

   The format string consists of ordinary byte characters (except %), which are copied
   unchanged into the output stream, and conversion specifications. Each conversion
   specification has the following format:

     * introductory % character.

     * (optional) one or more flags that modify the behavior of the conversion:

     * -: the result of the conversion is left-justified within the field (by default
       it is right-justified).
     * +: the sign of signed conversions is always prepended to the result of the
       conversion (by default the result is preceded by minus only when it is
       negative).
     * space: if the result of a signed conversion does not start with a sign
       character, or is empty, space is prepended to the result. It is ignored if +
       flag is present.
     * #: alternative form of the conversion is performed. See the table below for
       exact effects otherwise the behavior is undefined.
     * 0: for integer and floating-point number conversions, leading zeros are used to
       pad the field instead of space characters. For integer numbers it is ignored if
       the precision is explicitly specified. For other conversions using this flag
       results in undefined behavior. It is ignored if - flag is present.

     * (optional) integer value or * that specifies minimum field width. The result is
       padded with space characters (by default), if required, on the left when
       right-justified, or on the right if left-justified. In the case when * is used,
       the width is specified by an additional argument of type int, which appears
       before the argument to be converted and the argument supplying precision if one
       is supplied. If the value of the argument is negative, it results with the -
       flag specified and positive field width (Note: This is the minimum width: The
       value is never truncated.).

     * (optional) . followed by integer number or *, or neither that specifies
       precision of the conversion. In the case when * is used, the precision is
       specified by an additional argument of type int, which appears before the
       argument to be converted, but after the argument supplying minimum field width
       if one is supplied. If the value of this argument is negative, it is ignored. If
       neither a number nor * is used, the precision is taken as zero. See the table
       below for exact effects of precision.

     * (optional) length modifier that specifies the size of the argument (in
       combination with the conversion format specifier, it specifies the type of the
       corresponding argument).

     * conversion format specifier.

   The following format specifiers are available:

Conversion   Explanation                                          Expected
Specifier                                                       Argument Type
          Length               hh                                       ll        j        z        t
         Modifier→                      h      \fI(none)\fP        l                                               L
                            \fI(C++11)\fP                                  (C++11)   (C++11)  (C++11)  (C++11)
           Writes literal
           %. The full
    %      conversion       N/A      N/A      N/A      N/A           N/A      N/A       N/A     N/A        N/A
           specification
           must be %%.
           Writes a single
           character.

           The argument is
           first converted
           to unsigned
           char. If the l
    c      modifier is      N/A      N/A      int      wint_t        N/A      N/A       N/A     N/A        N/A
           used, the
           argument is
           first converted
           to a character
           string as if by
           %ls with a
           wchar_t[2]
           argument.
           Writes a
           character string

           The argument
           must be a
           pointer to the
           initial element
           of an array of
           characters.
           Precision
           specifies the
           maximum number
           of bytes to be
           written. If
           Precision is not
           specified,
           writes every
    s      byte up to and   N/A      N/A      char*    wchar_t*      N/A      N/A       N/A     N/A        N/A
           not including
           the first null
           terminator. If
           the l specifier
           is used, the
           argument must be
           a pointer to the
           initial element
           of an array of
           wchar_t, which
           is converted to
           char array as if
           by a call to
           wcrtomb with
           zero-initialized
           conversion
           state.
           Converts a
           signed integer
           into decimal
           representation
           [-]dddd.

           Precision
           specifies the
           minimum number
           of digits to
    d      appear. The      signed   short    int      long          long     intmax_t  signed  ptrdiff_t  N/A
    i      default          char                                     long               size_t
           precision is 1.

           If both the
           converted value
           and the
           precision are 0
           the conversion
           results in no
           characters.

           Converts an
           unsigned integer
           into octal
           representation
           oooo.

           Precision
           specifies the
           minimum number
           of digits to
           appear. The
           default
           precision is 1.
           If both the
           converted value
           and the
           precision are 0
    o      the conversion                                                                                  N/A
           results in no
           characters. In
           the alternative
           implementation
           precision is
           increased if
           necessary, to
           write one
           leading zero. In
           that case if
           both the
           converted value
           and the
           precision are 0,
           single 0 is
           written.

           Converts an
           unsigned integer
           into hexadecimal
           representation
           hhhh.

           For the x
           conversion
           letters abcdef
           are used.                                                 unsigned                   unsigned
           For the X        unsigned unsigned unsigned unsigned long long     uintmax_t size_t  version of
           conversion       char     short    int                    long                       ptrdiff_t
           letters ABCDEF
           are used.
           Precision
           specifies the
           minimum number
    x      of digits to                                                                                    N/A
    X      appear. The
           default
           precision is 1.
           If both the
           converted value
           and the
           precision are 0
           the conversion
           results in no
           characters. In
           the alternative
           implementation
           0x or 0X is
           prefixed to
           results if the
           converted value
           is nonzero.

           Converts an
           unsigned integer
           into decimal
           representation
           dddd.

           Precision
           specifies the
           minimum number
           of digits to
    u      appear. The                                                                                     N/A
           default
           precision is 1.
           If both the
           converted value
           and the
           precision are 0
           the conversion
           results in no
           characters.

           Converts
           floating-point
           number to the
           decimal notation
           in the style
           [-]ddd.ddd.

           Precision
           specifies the
           exact number of
           digits to appear
           after the
    f      decimal point
    F      character. The   N/A      N/A                             N/A      N/A       N/A     N/A
           default
           precision is 6.
           In the
           alternative
           implementation
           decimal point
           character is
           written even if
           no digits follow
           it. For infinity
           and not-a-number
           conversion style
           see notes.
           Converts
           floating-point
           number to the
           decimal exponent
           notation.

           For the e
           conversion style
           [-]d.ddde±dd is
           used.
           For the E
           conversion style
           [-]d.dddE±dd is
           used.
           The exponent
           contains at
           least two
           digits, more
           digits are used
           only if
           necessary. If
    e      the value is 0,  N/A      N/A                             N/A      N/A       N/A     N/A
    E      the exponent is
           also 0.
           Precision
           specifies the
           exact number of
           digits to appear
           after the
           decimal point
           character. The
           default
           precision is 6.
           In the
           alternative
           implementation
           decimal point
           character is
           written even if
           no digits follow
           it. For infinity
           and not-a-number
           conversion style
           see notes.
           Converts
           floating-point
           number to the
           hexadecimal
           exponent
           notation.

           For the a
           conversion style
           [-]0xh.hhhp±d is
           used.
           For the A
           conversion style
           [-]0Xh.hhhP±d is
           used.
           The first
           hexadecimal
           digit is not 0
           if the argument
           is a normalized
           floating-point
           value. If the                      double   double\fI(C++11)\fP                                       long
    a      value is 0, the                                                                                 double
    A      exponent is also N/A      N/A                             N/A      N/A       N/A     N/A
           0. Precision
 \fI(C++11)\fP   specifies the
           exact number of
           digits to appear
           after the
           hexadecimal
           point character.
           The default
           precision is
           sufficient for
           exact
           representation
           of the value. In
           the alternative
           implementation
           decimal point
           character is
           written even if
           no digits follow
           it. For infinity
           and not-a-number
           conversion style
           see notes.

           Converts
           floating-point
           number to
           decimal or
           decimal exponent
           notation
           depending on the
           value and the
           precision.

           For the g
           conversion style
           conversion with
           style e or f
           will be
           performed.
           For the G
           conversion style
           conversion with
           style E or F
           will be
           performed.
           Let P equal the
           precision if
           nonzero, 6 if
           the precision is
           not specified,
           or 1 if the
           precision is 0.
           Then, if a
           conversion with
           style E would
    g      have an exponent
    G      of X:            N/A      N/A                             N/A      N/A       N/A     N/A

             * if P > X ≥
               −4, the
               conversion
               is with
               style f or F
               and
               precision P
               − 1 − X.
             * otherwise,
               the
               conversion
               is with
               style e or E
               and
               precision P
               − 1.

           Unless
           alternative
           representation
           is requested the
           trailing zeros
           are removed,
           also the decimal
           point character
           is removed if no
           fractional part
           is left. For
           infinity and
           not-a-number
           conversion style
           see notes.
           Returns the
           number of
           characters
           written so far
           by this call to
           the function.

           The result is    signed                                   long               signed
    n      written to the   char*    short*   int*     long*         long*    intmax_t* size_t* ptrdiff_t* N/A
           value pointed to
           by the argument.
           The
           specification
           may not contain
           any flag, field
           width, or
           precision.
           Writes an
           implementation
           defined
    p      character        N/A      N/A      void*    N/A           N/A      N/A       N/A     N/A        N/A
           sequence
           defining a
           pointer.

   The floating-point conversion functions convert infinity to inf or infinity. Which
   one is used is implementation defined.

   Not-a-number is converted to nan or nan(char_sequence). Which one is used is
   implementation defined.

   The conversions F, E, G, A output INF, INFINITY, NAN instead.

   Even though %c expects int argument, it is safe to pass a char because of the
   integer promotion that takes place when a variadic function is called.

   The correct conversion specifications for the fixed-width character types (int8_t,
   etc) are defined in the header <cinttypes> (although PRIdMAX, PRIuMAX, etc is
   synonymous with %jd, %ju, etc).

   The memory-writing conversion specifier %n is a common target of security exploits
   where format strings depend on user input and is not supported by the bounds-checked
   printf_s family of functions.

   There is a sequence point after the action of each conversion specifier; this
   permits storing multiple %n results in the same variable or, as an edge case,
   printing a string modified by an earlier %n within the same call.

   If a conversion specification is invalid, the behavior is undefined.

.SH Return value

   1-3) Number of characters written if successful or negative value if an error
   occurred.
   4) Number of characters written if successful or negative value if an error
   occurred. If the resulting string gets truncated due to buf_size limit, function
   returns the total number of characters (not including the terminating null-byte)
   which would have been written, if the limit was not imposed.

.SH Notes

   All these functions invoke va_arg at least once, the value of arg is indeterminate
   after the return. These functions do not invoke va_end, and it must be done by the
   caller.

.SH Example


// Run this code

 #include <cstdarg>
 #include <cstdio>
 #include <ctime>
 #include <vector>

 void debug_log(const char *fmt, ...)
 {
     std::time_t t = std::time(nullptr);
     char time_buf[100];
     std::strftime(time_buf, sizeof time_buf, "%D %T", std::gmtime(&t));
     std::va_list args1;
     va_start(args1, fmt);
     std::va_list args2;
     va_copy(args2, args1);
     std::vector<char> buf(1 + std::vsnprintf(nullptr, 0, fmt, args1));
     va_end(args1);
     std::vsnprintf(buf.data(), buf.size(), fmt, args2);
     va_end(args2);
     std::printf("%s [debug]: %s\\n", time_buf, buf.data());
 }

 int main()
 {
     debug_log("Logging, %d, %d, %d", 1, 2, 3);
 }

.SH Output:

 04/13/15 15:09:18 [debug]: Logging, 1, 2, 3

.SH See also

   printf
   fprintf                   prints formatted output to stdout, a file stream or a
   sprintf                   buffer
   snprintf                  \fI(function)\fP
   \fI(C++11)\fP
   vscanf
   vfscanf                   reads formatted input from stdin, a file stream or a
   vsscanf                   buffer
   \fI(C++11)\fP                   using variable argument list
   \fI(C++11)\fP                   \fI(function)\fP
   \fI(C++11)\fP
   vprint_unicode            prints to Unicode capable stdout or a file stream using
   vprint_unicode_locking    type-erased argument representation
   (C++23)                   \fI(function)\fP
   (C++23)
   vprint_nonunicode         prints to stdout or a file stream using type-erased
   vprint_nonunicode_locking argument representation
   (C++23)                   \fI(function)\fP
   (C++23)
   C documentation for
   vprintf,
   vfprintf,
   vsprintf,
   vsnprintf
